Many electronic devices, such as smart phones and tablets, integrate biometric devices for the purpose of user authentication. The biometric devices can include, for example, iris scanners and camera systems capable of supporting iris identification functions, as well as additional functions such as facial recognition and gesture or motion recognition. However, iris scan systems have a number of limitations, especially those related to user variability, for example variability in iris color for several users of the device. Iris color is a result of differential absorption of light incident on pigmented cells in the outermost layer of the iris. A lesser amount of pigmentation results in less absorption and more light being reflected from the inner layers of the iris. Scattering during transmission of reflected light through the outer layer dictates perceived iris color, for example, a blue iris appearance. Higher levels of pigmentation lead to progressively darker iris coloring, with a dark brown iris appearance occurring at the upper end of high pigmentation levels.
An iris scan system optimized for one type of iris (e.g., iris color) can have limited functionality for a different type of iris, for example, optimization for a blue iris can limit capability for recognition of a brown iris. This can result in the iris scan system failing to correctly identify a user of the device.
Presently there are many variations of iris scan camera systems that function to capture images of the iris. Biometric iris scan camera systems that can be implemented on a mobile device face a number of challenges for effective operation. Several of these challenges include: iris variability (e.g. a user can have an iris color that is brown, blue, green, or another color); iris obstructions (e.g. eyelids, eyelashes, and other inherent features of the user can interfere with obtaining an image of the iris); ambient illumination (e.g. operation in full sunlight or in the presence of a strong optical noise source); motion blur (e.g. caused by eye saccades or other motions either controlled or involuntary); depth of field at close distances (e.g. images obtained at less than the camera systems intended focal length); additional cost and additional space for a biometric iris scan system, and; limited field of view. For reliable identification the camera must capture an image with resolution compatible with, for example, an approximately 200-row by 200-column line scan of the iris. The iris is typically only 10-12 mm in diameter, while the distance between the camera and the iris is considerable, typically approximately 40-50 cm; therefore, the camera capture area must be properly positioned on the face and iris area. A biometric iris scan camera system that is capable of addressing these issues would be advantageous.